1. Field of the Invention
The present disclosure relates to a sensor signal processing circuit connected to a capacitance type sensor, and a sensor signal processing method.
2. Description of the Related Art
Position detecting devices such as touch panels have come into wide use, and various inventions related to the position detecting devices have been made. For example, Patent Document 1 (Japanese Patent Laid-Open No. 2011-243081) discloses an invention related to a capacitance type position detecting device. The position detecting device disclosed in Patent Document 1 includes a sensor having a plurality of first conductors arranged in a first direction and a plurality of second conductors arranged in a direction different from the first direction, for example a second direction orthogonal to the first direction, and includes a sensor signal processing circuit connected to the sensor.
The sensor signal processing circuit of the position detecting device in this Patent Document 1 supplies a predetermined signal to the first conductors (transmitting conductors) of the sensor to detect a position indicated by an indicator. At the position indicated by a finger as the indicator on the sensor, a current (charge) corresponding to the predetermined signal is shunted via the finger, and thereby a capacitance (mutual capacitance) formed between a first conductor (transmitting conductor) and a second conductor (receiving conductor) changes. The sensor signal processing circuit can detect the position indicated by the finger as the indicator by detecting a change in the signal in the receiving conductor based on the change in the capacitance (mutual capacitance).
Incidentally, a position indicated by a position indicator (capacitance type pen-shaped position indicator (passive capacitive pen)) rather than a finger which position indicator a user holds with a hand to indicate the position on a sensor can also be detected by detecting a change in a signal in a receiving conductor based on a change in capacitance (mutual capacitance) on similar principles.
In addition, a position indicator referred to as an active capacitive pen is also known as an indicator. Known types of this active capacitive pen include a type of active capacitive pen that includes a driving power supply and an oscillator driven by the driving power supply within a casing of the active capacitive pen and which supplies an oscillating signal of the oscillator to the position detecting device, or a type of active capacitive pen that receives a signal from the position detecting device, amplifies the signal, and supplies the signal to the position detecting device. The position detecting device receiving the signal sent out from this type of position indicator detects a position indicated by the active capacitive pen by receiving the signal from the active capacitive pen by each of a first conductor in the first direction and a second conductor in the second direction of the sensor on the basis of capacitive coupling.
The conventional position detecting device detects a position indicated by the finger as an indicator, the passive capacitive pen, or another indicator by detecting a change in mutual capacitance in regions (cross point regions) formed between the plurality of first conductors arranged in the first direction and the plurality of second conductors arranged in the second direction. The detection of the position indicated by the indicator is performed in the conventional position detecting device irrespective of whether the finger or the passive capacitive pen is present at a position in proximity to the sensor such that the position indication may be performed on the sensor. That is, even when the indicator is in a state of being slightly distant from the sensor, or in a so-called hovering state, the hovering position of the indicator is detected by detecting a change in mutual capacitance.
However, the constitution that detects a position indicated by the indicator by detecting a change in mutual capacitance in the regions (cross point regions) formed between the plurality of first conductors arranged in the first direction and the plurality of second conductors arranged in the second direction has low detection sensitivity, and cannot necessarily be said to be most suitable in terms of detection sensitivity in a direction of height from the surface of the sensor in detecting the position indicated by the indicator in a hovering state.